Thermographic copying sheet



United States Patent 6 Claims. (Cl: 117-36.8)

ABSTRACT OF THE DISCLOSURE This invention relates to the reproduction of originals on heat sensitive copying materials by color thermography, using the heat-sensitive copying paper that contains heatsensitive compounds which form azomethine dyes when heated.

It is known in color thermographic methods to use copying materials containing compounds which undergo color change when heated either by absorption of radiant heat such as infrared rays, or by transfer of thermal energy by contact. In addition to this chemical method of producing an image, other methods based on physical principles are used. For example, an image may be produced by melting an opaque surface to render it transparent. In other processes, certain parts of the layer are imagewise fixed under the influence of heat, While the parts of the layer not affected by the heat can be removed.

It is among the objects of the present invention to provide new compounds for color thermography. The more specific object is to provide materials which yield upon exposure to a heat pattern a colored image of excellent quality. We have found that compounds having the activated methylene structure of a photographic color coupler, but in which structure one hydrogen of the activated methylene is substituted with an acylamino group derived from an aliphatic carboxylic acid and the other hydrogen atom of the methylene is substituted With a pamino phenylene imino grouping which is linked to the carbon atom of the methylene by the nitrogen atom of the imino group, exhibit excellent utility for color thermoprinting. The above compounds are colorless and upon the action of heat form azomethine dyes, the acylamino group is Splitting 01f.

Suitable compounds are derived from photographic color couplers containing activated open-chain or cyclic methylene groups. Those compounds are characterized by the following formulae:

wherein A and B are negative groups such as COR COOR CO.COOR -CO.NHR CO.NR R -CN; R stands for substituted or unsubstituted alkyl having up to 18 carbon atoms such as methyl, ethyl, allyl, butyl, dodecyl, octadecyl, and aryl such as phenyl, chlorophenyl, tolyl; a cycloalkyl group such as cycllopentyl, cyclohexyl, methylcyclohexyl; or an aralkyl group such as a benzyl group.

Compounds of this constitution are for instance acyl acetic esters, such as benzoylacetic esters, acyl acetoacetic esters, malonic acid ester, acyl acetonitriles, aroyl acetonitriles, cyanacetophenone, benzoylacetophenones, cyanacetic esters or acylacetic amides such as benzoy-lacet- 3,409,457 Patented Nov. 5, 1968 ice anilides which are substituted in the reactive methylene group by the radicals X and Y.

wherein D represents ring members necessary to complete a heterocyclic ring having adjacent to the carbonyl group an activated methylene group, the hydrogen atoms of which are substituted by the radicals X and Y.

Examples of such heterocyclic rings are compounds which are generally referred to as photographic magenta couplers. These couplers particularly include pyrazolone structures particularly l-phen-ylpyrazolones such as described in the publication of O. Wahl in Zeitschrift fiir angewandte Chemie, vol. 64 (1952), pages 259/265, indazolones or benzimidazolo pyrazolones such as described in British Patent No. 918,128. Y represents an acylamino group which is linked to the carbon atom by the nitrogen atom of the amino group and which is derived from aliphatic carboxylic acids preferably carboxylic acid having up to carbon atoms.

X stands for a p-aminophenylene imino grouping hav ing an unsubstituted imino group and which is linked to the carbon atoms by the nitrogen atom of the unsubstituted imino group. The p-amino group can be substituted in particular by alkyl groups having up to 5 carbon atoms which in turn can be substituted by carboxyl groups, hydroxy groups or sulfo groups and the like. The phenyl ring also can be substituted for example with alkyl in particular lower alkyl having up to 3 carbon atoms, halogen atoms in particular chlorine, alkoxy groups having up to 5 carbon atoms and the like. The substituents are preferably in o-position to the unsubstituted imino group.

The above compounds are prepared by reacting color couplers having an activated methylene group which is substituted with an amino group, with an acid anhydrid or acid chloride, preferably in the presence of pyridine, and then reacting the resulting acyl-amino-group containing color coupler under oxidizing conditions with a pphenylene diamine or derivatives thereof which contain 1 primary amino group. The preparation can :be illustrated by the following equation:

Under the action of heat compounds of the last mentioned formula decompose to form an azomethine dye 3; and "an" aliphatic "carbonarnide; according -to the followingeqoationzw w N'Ha.

senor be substituted as described ere A M ho s pmahs htiafie l of thecolqr couplers with an 'a r. Reference is..als o"mad e to British PatenpNo. 91; ,129 and U.S. Patent No. 3,079,255. As to the introduction of the acyl groups,'reference is inadeto the follow/ling examples orto Germah Patent 1,178,075. Theip'r'ep aration 'of the various color couplers having an acti vated Well known and need bedescribed' methylene structure is indetail. v

and acetoacetic esters concerned are pro- The benzoyl duced in a manner analogous to that given in CanJJ. Chem. 3l, 1025 (1953). The corresponding pyra'z olo'nes can be synthesiaed ir'ila generally knov'vnmanner by condensatiori ofthe c orrespon'din'g zit-substituted benzo'yl and acetoacetic este'rs with'phenyl hydfazines. j a

As p-phenylene dia-rnine compounds which are reacted with the acyl amino substituted color couplers 'un'der'fox; idizing conditions, there can be used all compoundswhich are known as color-forming developers capableffof re acting with color couplers the active methylene'g'roup ofwhich is unsubstituted with formation of azomethine dyes. Examples of su'ch compounds are'p-dietlfyladiinm aniline, p-dimethylaminoahiline, 2-methyl-4-diethylamirib aniline, p-dihydroxyethylaminoaniline and p-ethylsulfobutylaminoaniline.

The coupling by oxidation of the indicated components with the various acylamin'osubstituted color couplers is performed preferably in an inert solvent, advantageously at temperatures below C. in effective contact with an oxidizing agent such as hydrogen peroxide. Water or mixtures of water and water-soluble organic compounds such as lower alcohols, can for example, be used as reaction medium.

The colorless reaction product which can also be called leuco compounds can be isolated and are soluble in organic solvents, e.g., methanol or dimethylforrnamide, or if substituted with acid groups, in aqueous alkalis. They are transformed into yellow or violet azomethine dyes upon being heated to temperatures of about 100'- 160 C., whether in solid form, in solution or after being applied to a suitable support material, such as paper. A conversion of the leuco compounds into the azomethine dyes can be accelerated by using alkalis, such as alkali alcoholates. The leuco compounds are suitable for the production of heat-sensitive printing materials which permit reproduction of an image 'with the aid of infrared radiation or by contact transfer of heat energy.

The heat-sensitive compounds of the present invention are conveniently applied to a sheet-like support in the form of a dispersion or solution in a suitable volatile solvent either alone or in combination with a film-forming binding agent such as cellulose ester of inorganic or organic acids, for example nitro cellulose or cellulose acetate, polyvinyl butyral, polyvinyl alcohol, cyclized rubber and the like. The binding agent assists in retainunderstood in th ing' ith'e heat-sensitive compound *n thdsurface of the' support' Thinpaper "sheets are the preferred supporting material for the heat-sensitive coating, the sheet material however need only be r transparenttm 'thenadianb "energy of the wave' length employed in the ther-mogr'aphiw roces's-.-" '0ther'film-or-" sheet materiaIs'capable' of be'ing"pen'e trated by 'theradiant energycan be used; such s any fo-rnr'ing' binding hgents suclr as fori exar-npley cellulose esters, "can be" used ==as 'a. self-supportingfilmseontaining th'e filrri-lforming binding-agentand the heat-sensitive compound. Thdusual source'sqof radiation mayibe used in' the"p rese'nt'therrnographic boating process. These iw elude, by way of example; high intensity incandescent lamps; ph'otofiashlamps; electric arc lamps,=.-high energy infrared lamps- 'and tlre' like. The:heat-sensitivercopying material- "of the present invention may fibe utilized: 1 :for contact printing, refiex pr inting or the' inscribingof m'arke ings by means"of'beatedstylus'or heate'd stamps,all-well e thermographic printing artix:

(a) VPreparation. of; the colorless leuco compound the formula; f

solution of 13.1 of pdiethylfaminoai iiline"sulfate ih'200 c'c. 0f water vvas added' to "a s'oluti1ori of 19.4 g; If acetylamino py'rai ololT;5a)-behzimidai- V ul'fonic acid 'andi g ""of" anhydrous; sodiirm carbonate inl50 cci'of'" atergiwhi l e stirring, a solut n off 5,.66 cc. j of hydrogen peroxide "'(30%")'in"-50" cc. of water is added dropwise and the reactioir'r nixture" is' l'eft to stand for one 'hour. The sodium salt which crystallizes out is suction-filtered, stirred with 50 cc. of hydrochloric acid, once again suction-filtered and washed with water until the filtrate is colorless. About 15 g. of product of the above formula are obtained.

Upon heating it changes color at C., with decomposition above 230 C. Empirical formula C2'1H2gO4N6S'3H20; molecular weight 584.

Calculated: C, 55.29%; H, 5.80%; O, 19.11%; N, 14.33%; S, 5.46%. Found by analysis: C, 54.53%; H, 6.02%; O, 19.25%; N, 14.21%; S, 5.48%.

If a sample of this substance is heated in dimethylformarnide, a violet dye is formed.

(b) Production of the azomethine dye of the formula:

1 I 1 g. of the aboveleuco compound is stirred with 15 cc. of methanol, 5 cc. of 5% sodium methylate solution are added and the mixture heated for a short time on a steam bath. A reddish-violet dye solution is formed. This is neutralised with 40% acetic acid and the solvent is then distilled off in a water jet vacuum at room temperature. The residue is taken up in 250 cc. of water and the dye is precipitated by adding common salt. The dye is filtered off with suction and is taken up in methanol. After evaporating the solvent, about 0.7 g. of dye are obtained. M.P. decomposition 315 C.

Example 2 (a) Preparation of the colorless leuco compound of the formula: 1

A solution of 6.5 g. of -p-diethylaminoaniline sulfate in 100 cc. of water is added to a solution of g. of 2-phenyl 3-propionyl-amino-pyrazolo-(1,5a)-benzimidazole sulfonic acid-6 and g. of anhydrous sodium carbonate in 75 cc. of Water. A solution of 2.8 cc. of hydrogen peroxide (30%) in cc. of water is added dropWise thereto. The mixture is then left to stand for 1 /2 hours and then the product is precipitated by adding 3% hydrochloric acid, whereupon it is suction-filtered and washed with water until the discharging filtrate is colorless. About 8 g. of product in accordance with the above formula are obtained. Upon heating it changes color at 120 C. with decomposition above 220 C.

Empirical formula C H O N S-2H O; molecular weight 582.

Calculated: C, 57.73%; H, 5.84%; O, 16.49%; N, 14.43%; S, 5.89%. Found: C, 58.30%; H, 5.99%; O, 15.49%;N, 14.49%; S, 5.95%.

On heating a sample of the substance in dimethylformamide, a violet dye is also formed.

(b) Production of the azomethine dye.--1 g. of the above leuco compound is stirred into 15 cc. of methanol,

5 cc. of 5% sodium methylate solution are added and the mixture boiled for a short time. The sodium salt of the dye according to Example 1 precipitates and is suctionfiltered. Yield: about 0.7 g., M.P. decomposition 325 C.

Example 3 (a) Preparation of the colorless leuco compound of the formula:

C H: 6:0 11:11 /C2H5 C9115 r A "solutionof 6.5 g. of p-diethylaminoanaline sulfate in 150 cc. of water is added to a solution of 9.3 g. of 1- (4-sulfophenyl) 3-phenyl-4-acetylaminopyrazolone-S and 15 g. of anhydrousrsodium carbonate in 75cc. of water. To this mixture there is. added dropwise at room temperature and while stirring, a solution'of 2.8 cc. of hydrogen peroxide in 25 cc. of water. The mixture is left standing for 1 hour at room temperature and the ,addition compound is then precipitated with 3% hydro- 1 g. of the above leuco compound is heated to boiling point in 15 cc. of dimethylformamide until a dyestuif solution has been formed. The solvent is distilled off in water jet vacuum while heating gently. The residue is taken up in.10 cc. of methanol. After evaporating the solvent, about 0.8 g. of the azomethine dye are obtained.

EXAMPLE 4 (a) Preparation of the colorless leuco compound. A solution of 10.2 g. of p-diethylaminoaniline sulfate in 160 cc. of Water is added at room temperature to a solution of 9.24 g. of 1 phenyl 3 methyl 4 acetylaminopyrazolone 5 in cc. of 4% sodium hydroxide solution and 200 cc. of water. While stirring, a solution of 4.5 g. of hydrogen peroxide (30%) in 40 cc. of water is then added dropwise at 30 C. After standing overnight in a refrigerator, the substance is suction-filtered and washed neutral with water. About 6 g. of product are isolated. Upon heating it changes color at C., melting at -147" C. Empiral formula molecular weight 377.

Calculated: C, 65.78%; H, 7.16% O, 8.48%; N, 18.56%. Found: C, 66.03%; H, 7.16%; O, 8.39%; N, 18.08%.

On heating the substance in dimethylformamide, a violet dye is formed.

(b) Production of the azomethine dyestutf of the I w .4 9.45 r

' 1 g of the above leuco compound is dissolved in 15 cc. of methanol and 5 cc. of 5% sodium methylate solution are added. The mixture is boiled for a short time in a steam bath, the dye solution is made neutral with dilute acetic acid and concentrated in'a water jet vacuum at room temperature. The residue is taken up in water andthe azomethine dye is salted out with common salt. Yield'about0.7"g. Y l r i Example 5 v I al -Preparation of the colorless leuco compound of thenformula:

is stirred for another 45 minutes. It is then made neutral with 4% acetic acid and the formed addition product is filtered olf with suction. About 1.2 g. of product of the above formula are obtained.

Upon heating it changes color at 162 C. to form a yellow dyestuff, melting at 197 C.

(b) Production of the azomethine dye of the formula:

1 g. of the above leuco compound is stirred with 15 cc. of methanol, 5 cc. of 5% sodium methylate solution are added and the mixture heated for a short time in a steam bath. A brownish-yellow dye solution is formed. This is made neutral with 40% acetic acid and the solvent is distilled off in a water jet vacuum at room temperature. The residue is taken up in water, the dye is salted out by adding common salt and suction-filtered. The suction-filtered dye is taken up in methanol. After evaporating the solvent, about 0.8 g. of dye is obtained.

(c) The initial components for the production of the above leuco compound can be prepared as follows:

1 (4 methoxy)benzoylacetic acid (2" methoxy- 5" carboxy) anilide.A mixture of 55 g. of 3- amino 4 methoxybenzoic acid, 160 cc. of pyridine and 40 g. of ethyl p methoxybenzoyl acetate are heated while stirring to 125-130 C. Thereafter, within 3 to 4 hours and by adding another 39 g. of p methoxy benzoylacetate, 67.5 g. of alcohol-pyridine mixture are distilled off through a column. After again adding 8 g. of pmethoxy-benzoylacetate, another 6.7 g. of alcoholpyridine mixture are distilled off. The reaction mixture is cooled to 20 C. and the precipitated product is suction-filtered. This is stirred twice with acetone, using cc. on each occasion, and is then suction-filtered and washed with acetone until the filtrate runs off in clear form. About 54 g. of the last mentioned anilide are obtained. M.P. 256 C.

1 nitroso 1 (4' methoxy)benzoylacetic acid- (2" methoxy 5" carboxy)anilide.-l7 g. of the foregoing product are dissolved in 75 cc. of 4% sodium hydroxide solution, 35 cc. of 10% sodium nitrite solution are added thereto, the substance is filtered and introduced at 0C. into 50 cc. of 20% hydrochloric acid. The mixture is then stirred for 3 hours, the temperature being allowed to rise slowly to room temperature. The precipitated product is suction-filtered and, while still moist, is extracted by boiling with 250 cc. of methanol. About 12 g. of nitroso product are obtained. M.P. 280 C.

1,-amino 1 (4'-meth0xy)benzoylacetic acid-(2"-methoxy-5-carboxy) anilide-12 g. of the above nitroso product are stirred with 100 cc. of methanol and dissolved by adding 20 cc. of 25% ammonia. Hydrogenation takes place in the presence of Raney nickel for one hour at 50 C. and 50 atm. of H the substance is filtered off from the catalyst and the filtrate is made neutral with 20% sulphuric acid. After cooling, this is suction-filtered. The crude product is extracted by boiling with 200 cc. of water. About 9 g. of amine are obtained. M.P. 203 C.

l-acetamino-l-(4-methoxy)benzoylacetic acid-(2"-methoxy-5"-carboxy)anilide-6 g. of the foregoing amine are stirred for 15 minutes at l00 C. with 50 cc. of acetic anhydride. The mixture is left to stand overnight at room temperature and then the solvent is distilled off in water jet vacuum. The residue is boiled with cc. of methanol and allowed to cool while stirring. The product which crystallises out is suction-filtered, again stirred with 50 cc. of methanol in the cold and again suctionfiltered. Yield about 4 g. of acetyl product. M.P. 260 C.

The following examples illustrate the use of the leuco compounds obtainable according to the invention for the production of thermal copies.

Example 6 Absorbent writing paper (so-called absorbent post paper) is impregnated with a colution of 2 g. of the leuco compound according to Example 1 in 200 cc. of methanol and 2.5 cc. of 4% sodium hydroxide solution and dried. A heat-sensitive copying paper is obtained, which changes in colour to violet on heating to C. For producing images, the paper is either treated with a writing or marking instrument at a temperature of about C. or processed in a manner known per se in the so-called thermal copying apparatus. A brief strong infrared irradiation then takes place, which leads to a brief heating at the image areas of the original. The heat-sensitive copying paper which is in contact takes up this heat with formation of an image of the original.

Example 7 2 g.-of the leuco compound according to Example 2 are dissolved in 200 cc. of methanol and 3 cc. of 4% sodium hydroxide solution. The procedure is as in Example 6. The copying paper which is obtained changes to violet in colour on heating to 120 C.

Example 8 2 g. of the leuco compound according to Example 3 are dissolved in 200 cc. of methanol and 2 cc. of 4% sodium hydroxide solution. By following the procedure of Example 6, a copying paper is obtained which changes to violet in colour on heating to 160 C.

Example 9 2 g. of the'leuco compound according to Example 4 are dissolved in 200 cc. of methanol. The procedure followed is that set out in Example 6. The copying paper which is obtained changes to violet in colour on heating to C.

What I claim is:

1. In a thermographic copying material having a sheetlike support carrying a heat sensitive compound that changes in color upon heating, the improvement according to which said compound is a leuco form of an azomethane dye having a p-amino-phenylene-imino group substituted for a hydrogen of an active methylene in a photographic color coupler, the other hydrogen of the methylene being substituted by an acylamino group in which acyl is that of an aliphatic carboxylic acid having up to 5 carbons, and the imino portion of the p-aminophenylene-imino group is unsubstituted.

2. The combination of claim 1 in which the color coupler is a magenta pyrazolone coupler.

3. The combination of claim 1 in which the color coupler is a pyrazolo-(1,5a)-benzimidazo1e.

4. The combination of claim 1 in which the color coupler is a benzoylacetanilide.

5. The combination of claim 1 in which the p-amino portion of the p-amino-phenylene-imino group is substituted by alkyls having up to 5 carbon atoms, which alkyls can have carboxy, hydroxy or sulfo substituents.

6. The combination of claim 1 in which the phenylene portion of the p-amino-phenylene-imino group is substituted by alkyl having up to 3 carbon atoms, halogen, or alkoxy having up to 5 carbon atoms.

References Cited UNITED STATES PATENTS 2,976,294 3/ 1961 Firestine 96-90 3,219,470 11/1965 Lassig 117-368 3,293,061 12/1966 Lawton 117-368 3,312,551 4/1967 Sus 117-368 MURRAY KATZ, Primary Examiner. 

